Antibacterial Fresh-Keeping Films Assembled by Synergistic Interplay Between Casein and Shellac

With the strict demands by modern society of low-carbon, biodegradability, and eco-friendliness, developments of novel preservative films are required to replace the traditional ones. In this study, all-natural casein and shellac were co-assembled into homogeneous networks (CSFs), which was performed by simply dissolving both biopolymers at pH 12 followed by neutralization of the alkalinity. The replacement of calcium bridges in casein by shellac created more dexterity of the CSFs due to greater molecular flexibility of shellac than calcium, whereby contributing to promoted material elongation and toughness. To further enhance the moisture holding capacity, the CSFs were plasticized by glycerol, yielding smoother films (Gly-CSFs) with tensile strength and toughness being up to 3.55 MPa and 2.05 MJ/m3, respectively. The Gly-CSFs were then functionalized by eugenol (Eug-Gly-CSFs) to enable antioxidant and antibacterial properties. Based on rice cakes as the experimental models, the Eug-Gly-CSFs significantly retarded the mildew growth and extended the shelf-life of the rice cakes. This study utilized synergistic interplay between casein and shellac as a facile tool to assemble preservative films with biodegradability, bacteriostasis, and favorable mechanical properties.